Integrated circuits have become increasingly smaller, and consequently the process for electrically coupling such integrated circuits to other components (e.g., other integrated circuits) demands increasing precision. It is well known, for example, to produce electronic connections by means of soldering; i.e., melting alloy or chemical element with a relatively low melting temperature wherein the base materials of the workpieces being joined are not melted and do not become part of a joint. Alternatively, it is known to make electronic connections between components by means of welding. This involves the melting of the base workpieces to be joined resulting in the formation of a weld nugget comprised of material from both of the components being joined; i.e., by means of a fusion or mixing of the base metals. In such applications, heat is often employed to support the soldering or welding process; however, traditional heating methods have certain drawbacks when used in the microelectronic integrated circuit environment. That is, the application of heat to the bonding site typically involves either a bonding tool to convey heat to the bonding site or a heater block, which may be clamped to a circuit lead frame. Such processes, however, may result in distortion or bending of the lead frame or damage to the electronic components being joined especially if the heat source is large compared to the area being bonded.
Ribbon and wire bonders that utilize ultrasonic energy to bond conductive wires or ribbons to substrates, lead frames, or other components are also known. In this case, a bonding tool imparts high frequency vibrations to the parts being bonded resulting in metallurgical atomic diffusion bonding. Unfortunately, ultrasonic bonding suffers certain drawbacks. For example, ultrasonic or thermal-sonic (ultrasonic vibration in combination with the application of heat) bonding methods may find application in bonding flat, rigid structures, but are not well-suited to bond less rigid (flexible or semi-flexible) structures since such structures tend to vibrate in response to the ultrasonic energy resulting in loss of energy and therefore an inefficient process. Furthermore, the ultrasonic energy or vibration may cause unwanted movement of the parts being joined during the bonding process resulting in weaker and/or inconsistent bonds. In addition, ultrasonic bonding is typically only employed with certain metals such as gold, aluminum, and copper.
As a result of the limitations described above, known bonding techniques have given way to improved systems that utilize a laser to produce electrical interconnections by means of a connecting medium such as conductive ribbons or wires. One known laser bonding apparatus and method is described in U.S. Pat. No. 6,717,100 B2 entitled “Apparatus and Method for Laser Welding of Ribbons” issued Apr. 6, 2004 and assigned to the assignee of the present invention. This laser bonding apparatus positions a bonding tool over a first bonding site. A connecting medium, such as a conductive metal ribbon, is supplied from a standard spool, and the bonding tool is adapted to receive the ribbon through a guide slot that includes a ribbon entrance and a ribbon exit. The bonding tool is somewhat boot-shaped having a generally vertical leg or body portion and a forwardly extending foot portion having a laser aperture therethrough. In this known laser bonding apparatus, the bonding ribbon is guided through an opening in the leg or body portion and exits the leg portion at a point proximate the rear of the foot portion (i.e., the heel) where it is then threaded through a guide slot and beneath the bonding surface of the bond foot.
To produce a bond at a specific location, the bonding tool is maneuvered to that location such that the conductive ribbon is positioned between a lower or bonding surface of the foot portion and the substrate or component to which the ribbon is to be attached. The conductive ribbon is then exposed to a laser beam through the laser aperture in the foot portion to effectuate the required connection. After the ribbon is bonded to this first site, the laser ribbon bonding apparatus may move the bonding tool to a second bonding site to perform a second bonding operation thus electrically connecting the first bonding site to the second bonding site. As the bonding tool is moved to the second site, the ribbon, now secured to the first site, is pulled through the tool to form a connecting loop or strap. The laser bonding apparatus may repeat these steps to electrically connect addition sites, or the laser bonding apparatus may simply terminate the operation as, for example, by clamping the ribbon and performing a series of motions to break the ribbon proximate the last bonding site in the bonding sequence.
It should be appreciated that the quality and/or accuracy of a bond produced by a laser bonding apparatus of the type above described is significantly influenced by the degree to which the ribbon is properly aligned beneath the laser aperture. Because the ribbon enters the entrance of a guide slot at the rear of the bonding tool and exits the guide slot in the heel portion of the bonding tool it must then travel a significant distance to the laser aperture possibly resulting in misalignment of the ribbon beneath the laser aperture. This, in turn, may result in an improper or ineffective bond. In addition, the excessive length of travel can result in excessive ribbon slack. Last but not least, certain difficulties have been encountered when attempting to thread the ribbon into the ribbon entrance of the guide slot.
It should thus be appreciated that it would be desirable to provide a laser bonding apparatus configured to provide a more reliable presentation of the bonding ribbon beneath the laser aperture of a bonding tool. It would further be desirable to provide an improved bonding tool for use in a laser ribbon bonding system that is configured to reduce the distance that the ribbon must travel from the output of a guide channel proximate a bonding surface to a bonding position beneath a laser aperture. It would be still further desirable to provide a bonding tool for use in a laser ribbon bonding apparatus that is configured to facilitate threading the ribbon through a guide channel proximate a laser aperture for presentation beneath the laser aperture. Other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.